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• Layer melt crystallization of monoethylene glycol was investigated. • Impurity under study was 1,2-pentanediol and solvent additive acetone. • Thermodynamic driving forces with and without solvent additive were determined. • Crystallization kinetics affects purity of final product. Separation of glycols with close boiling points and relatively high viscosity at their melting point is a challenge in the production of high purity products downstream of biorefinery processes. In this work, the efficiency of the layer melt crystallization process with acetone as the assisting solvent was evaluated for a mixture of monoethylene glycol and 1,2-pentanediol. Solid-liquid equilibrium was measured and modelled with the NRTL and modified UNIFAC group-contribution models to evaluate the thermodynamic driving force of crystallization. Layer melt crystallization was conducted to determine the effect of solvent composition on purity, distribution coefficient of impurity, crystal growth rate, and yield at different operating conditions. Addition of the solvent altered the thermodynamics and kinetics of crystallization, thereby altering the purity level of the final product. An effective distribution coefficient of impurity between 0.1 and 0.6 in one-step crystallization was obtained, depending on the solvent composition and the applied operating conditions. [ABSTRACT FROM AUTHOR]

Natural freezing has the possible use to be used as a purification technique to treat wastewater. Natural freezing was simulated experimentally for ice crystallization from unsaturated Na 2 SO 4 (aq) solutions to assess the feasibility of such a technique for being used to purify wastewater. The influence of solution concentration and different growth conditions, such as ambient temperature, freezing time and freezing rate, on the efficiency of the purification process was investigated by analysis of the effective distribution coefficient ( K ) of the solute between the ice and the solution. A calculation method is introduced to estimate the concentration of solution at the advancing ice–solution interface in terms of the limiting distribution coefficient ( K ⁎ ) from experimental K values at different growth conditions. The heat transfer controlled growth rate of the ice limited by the free convective heat transfer coefficient of air ( h air ) rather than the thermal conductivity of the ice ( k ice ) and the heat transfer coefficient of the solution ( h sol ) found to prevail over the mass transfer of rejected solute molecules from the ice–solution interface to the bulk solution. Advancement of the thermal ( δ T ) and concentration boundary layer ( δ C ) at the ice–solution interface was proportional to the square root of freezing time. A simplified model is developed to estimate the thickness of the ice layer formed from solutions at different freezing conditions and the model is validated with experimental results. [ABSTRACT FROM AUTHOR]